For regulating the profile in a Yankee machine, an IR-dryer may be placed before the wet-end block of the hood, for example, so that the dryer becomes a part of the Yankee hood. For proper operation, the radiators of the IR-dryer must be cooled, which requires a certain amount of cooling air, whereby the ultimate temperature of the air rises to a level of about 80.degree. C. to about 100.degree. C.
Due to leakage of air and heat from the Yankee hood, the gap between the Yankee hood and the cylinder is a problematic and critical point. Penetration of very hot and moist air through the gap into the machine hall results in inferior working conditions and in higher consumption of energy. Also, when the leakage from the machine hall into the hood becomes excessive, the consumption of energy is additionally increased because the temperature of the circulation air and of the exhaust air is lowered.
It is generally difficult to regulate the leakage of air and heat because the plates obstructing the gap between the Yankee cylinder and hood do not operate efficiently. Since the air-conditioning of the hood is very difficult to regulate in a manner so that leakage is completely eliminated, small leakage from the machine hall into the hood is, as a rule, permitted because leakage into the hood is less detrimental than leakage in the outward direction. Therefore, there is generally a slight negative pressure in the gap between the Yankee cylinder and the hood, and the amount of leakage is, as a rule, from about 10 to about 15% of the exhaust air of the total block, which air is removed from the system.